@Configuration
public class CorsConfig implements GlobalFilter, Ordered {
  private static final String ALL = "*";
  private static final String MAX_AGE = "18000L";

  @Bean
  public RouteDefinitionLocator discoveryClientRouteDefinitionLocator(DiscoveryClient discoveryClient,
                                    DiscoveryLocatorProperties properties) {
    return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
  }

  @Bean
  public ServerCodecConfigurer serverCodecConfigurer() {
    return new DefaultServerCodecConfigurer();
  }
　　　//添加請求頭　
  @Bean
  public WebFilter corsFilter() {
    return (ServerWebExchange ctx, WebFilterChain chain) -> {
      ServerHttpRequest request = ctx.getRequest();
      if (!CorsUtils.isCorsRequest(request)) {
        return chain.filter(ctx);
      }
      HttpHeaders requestHeaders = request.getHeaders();
      ServerHttpResponse response = ctx.getResponse();
      HttpMethod requestMethod = requestHeaders.getAccessControlRequestMethod();
      HttpHeaders headers = response.getHeaders();
      headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN, requestHeaders.getOrigin());
      headers.addAll(HttpHeaders.ACCESS_CONTROL_ALLOW_HEADERS, requestHeaders.getAccessControlRequestHeaders());
      if (requestMethod != null) {
        headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_METHODS, requestMethod.name());
      }
      headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS, "true");
      headers.add(HttpHeaders.ACCESS_CONTROL_EXPOSE_HEADERS, ALL);
      headers.add(HttpHeaders.ACCESS_CONTROL_MAX_AGE, MAX_AGE);
      if (request.getMethod() == HttpMethod.OPTIONS) {
        response.setStatusCode(HttpStatus.OK);
        return Mono.empty();
      }
      return chain.filter(ctx);
    };
  }
　　//將請求頭中有多個值的去掉 這是該版本的一個bug
  @Override
  public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
    return chain.filter(exchange).then(Mono.defer(() -> {
      exchange.getResponse().getHeaders().entrySet().stream()
          .filter(kv -> (kv.getValue() != null && kv.getValue().size() > 1))
          .filter(kv -> (kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)
              || kv.getKey().equals(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS)))
          .forEach(kv -> {
            kv.setValue(new ArrayList<String>() {{
              add(kv.getValue().get(0));
            }});
          });

      return chain.filter(exchange);
    }));
  }

  @Override
  public int getOrder() {
    // 指定此過濾器位于NettyWriteResponseFilter之后
    // 即待處理完響應體后接著處理響應頭
    return NettyWriteResponseFilter.WRITE_RESPONSE_FILTER_ORDER + 1;
  }
}